Anodes for mercury-cathode electrolytic cells

Claim 2

A PROCESS FOR FORMING IMPROVED ANODES FOR MERCURYCATHODE ELECTROLYTIC CELLS, BY FORMING ON AN ANODE AN ANODICALL-CONDUCTING OXIDIC COATING HAVING A POROUS OUTER LAYER OF A CHLORINE RESISTANT POLYMER BOND THERETO, SAID POLYMER BEING POLYVINYLIDENE FLUORIDE OR LOW MOLECULAR WEIGHT POLYTETREFLUOROETHYLENE, THE PROCESS COMPRISING COATING THE ANODE WITH THE OXIDIC COATING, WHEREIN THE OXIDIC COATING COMPRISES A PLATINUM GTOUP METAL OXIDE, APPLYING TO SAID OXIDI COATING THE POLYMER IN ADMIXTURE WITH A REMOVABLE SOLID PARTICULATE MATERIAL, WHEREIN SAID SOLID PARTICULATE MATERIAL IS AN ALKALI METAL CHLORIDE, STARCH, CELLULOSE, A WATER INSOLUBLE BASE OR CARBONATE THEREOF, BONDING THE POLYMER TO THE OXIDIC COATING BY SUCCESSIVE STAGES OF DRYING BY HEATING IN AIR AT ABOUT 160*C, HEATING TO MELT THE POLYMER AT TEMPERATURES OF UP TO 280*C, AND COOLING, AND SUBSEQUENTLY REMOVING THE SOLID PARTICULATE MATERIAL FROM THE COATING BY DISSOLVING THE PARTICULATE MATERIAL BY DISSOLVING IN WATER OR DILUTE ACID, WHEREBY THE SHORTCIRCUIT CURRENT BETWEEN THE ANODE AND THE MERCURY CATHODE AT ANY GIVEN IMPRESSED VOLTAGE IS REDUCED WITHOUT PREVENTING PASSAGE OF THE ELECTROLYZING CURRENT UNDER NORMAL OPERATING CONDITIONS.

Claim 3

A process as claimed in claim 1 wherein the solid particulate material is an alkali metal chloride, starch or cellulose.

Claim 4

A process as claimed in claim 1 wherein the solid particulate material is removed by reaction in the electrolytic cell soon after the anode is put on service.

Claim 5

A process as claimed in claim 1 wherein the solid particulate material is a water-insoluble inorganic base or carbonate.

Claim 6

A process as claimed in claim 4 wherein the solid particulate material is calcium carbonate.

Claim 7

A process as claimed in claim 4 the solid particulate material is removed by dissolving in acid or by reaction in the electrolytic cell soon after the anode is put in service.

Claim 8

A process as claimed in claim 1 wherein the oxidic coating comprises a platinum group metal or oxide thereof in admixture with an oxide of a film forming metal.

Claim 9

A process as claimed in claim 7 wherein the oxidic coating comprises ruthenium dioxide and titanium dioxide.

Claim 10

The process of claim 1, wherein the thickness of the polymer coating is up to 5 g/m2.

Claim 11

An anode for a mercury cathode electrolytic cell, comprising a support member made of titanium or a film-forming titanium alloy and bonded thereto an anodically-conducting oxidic coating, said coating being a platinum group metal or an oxide thereof, having a porous outer layer of a chlorine-resistant organic polymer bonded thereto, said polymer being polyvinylidene fluoride or low molecular weight Polytetrafluoroethylene, and wherein the anode is coated by the process claimed in claim 1.

Claim 12

A process for producing an improved anode for mercury-cathode electrolytic cells, by forming on an anode anodically-conducting oxidic coating having a porous outer layer of a chlorine resistant polymer bonded thereto, said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating, wherein the oxidic coating comprises a platinum group metal oxide; coating the said oxidic coating with a discontinuous layer of solid particulate material, wherein said solid particulate material is an alkali metal chloride, starch, cellulose, a water insoluble base or carbonate thereof, so that a fraction of the oxidic coating is left uncovered between individual particles of the particulate material; coating with the polymer so as to fill the spaces between the particles; bonding the polymer to the oxide by heating at temperatures up to 280*C to melt the polymer, followed by cooling; and subsequently removing the solid particulate material from the coating by dissolving in water or dilute acid, whereby the short-circuit current between the anode and the mercury cathode at any given impressed voltage is reduced without preventing passage of the electrolyzing current under normal operating conditions.

Claim 13

A process for producing an improved anode for mercury-cathode electrolytic cells, by forming on an anode anodically-conducting oxidic coating having a porous outer layer of a chlorine resistant polymer bonded thereto, said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating, wherein the oxidic coating comprises a platinum group metal oxide; coating the said oxidic coating with a discontinuous layer of solid particulate material, wherein said solid particulate material is an alkali metal chloride, starch, cellulose, a water insoluble base or carbonate thereof, so that a fraction of the oxidic coating is left uncovered between individual particles of the particulate material; coating with the polymer so as to fill the spaces between the particles; bonding the polymer to the oxide by heating at temperatures up to 280*C to melt the polymer, followed by cooling; and subsequently removing the solid particulate material from the coating by dissolving in water or dilute acid, whereby the short-circuit current between the anode and the mercury cathode at any given impressed voltage is reduced without preventing passage of the electrolyzing current under normal operating conditions.

Claim 14

A process as claimed in claim 11 wherein the anodically-conducting oxidic coating comprises a platinum group metal oxide.

Claim 15

The process of claim 11, wherein the thickness of the polymer coating is up to 5 g/m2.

Claim 16

A process as claimed in claim 11, wherein the oxidic coating comprises ruthenium dioxide and titanium dioxide.

Claim 17

A process for forming on an anode an anodically conducting oxidic coating have a porous outer layer of a chlorine-resistant polymer bonded thereto said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating said oxidic coating being a platinum group metal oxide, heating the coated anode to about 250*C, spraying molten polymer on to the oxide layer and allowing the coated anode to cool.

Claim 18

A process for forming on an anode an anodically conducting oxidic coating have a porous outer layer of a chlorine-resistant polymer bonded thereto said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating said oxidic coating being a platinum group metal oxide, heating the coated anode to about 250*C, spraying molten polymer on to the oxide layer and allowing the coated anode to cool.

Claim 19

A process for forming on an anode an anodically conducting oxidic coating having a porous outer layer of a chlorine-resistant polymer bonded thereto said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating said oxidic coating being a platinum group metal oxide, applying to the said coating the polymer in a liquid vehicle, removing the liquid vehicle by evaporation, and heating the coated anode to about 250*C to melt the polymer coating, and allowing the coated anode to cool.

Claim 20

A process for forming on an anode an anodically conducting oxidic coating having a porous outer layer of a chlorine-resistant polymer bonded thereto said polymer being polyvinylidene fluoride or low molecular weight polytetrafluoroethylene, the process comprising coating the anode with the oxidic coating said oxidic coating being a platinum group metal oxide, applying to the said coating the polymer in a liquid vehicle, removing the liquid vehicle by evaporation, and heating the coated anode to about 250*C to melt the polymer coating, and allowing the coated anode to cool.